Power control method and apparatus in wireless access system

ABSTRACT

The present invention provides methods for transmitting a scheduling request (SR) in a wireless access system supporting a multiple connection mode, in which a terminal is connected to two or more small cells, and apparatuses supporting the same. According to one embodiment of the present invention, a method for transmitting an SR, by a terminal, in a wireless access system supporting a multiple connection mode comprises the steps of: receiving an upper layer signal including an SR parameter for SR transmission from a first small cell which is in a multiple connection mode state; generating an SR on the basis of the SR parameter; and transmitting the SR using a physical uplink control channel (PUCCH) signal. Herein, the SR parameter is pre-set by negotiation between the first small cell and a second small cell which is in a multiple connection mode. Furthermore, in the multiple connection mode, the terminal maintains multiple connections with two or more small cells including the first small cell and the second small cell, and the first small cell and the second small cell may be connected to each other via a non-ideal backhaul link.

TECHNICAL FIELD

The present invention relates to a radio access system and, moreparticularly, to a method for controlling transmit power in anenvironment, in which a user equipment (UE) is connected to two or moresmall cells, and an apparatus supporting the same.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

Recently, the structure of a radio access system has changed to astructure in which small cells (e.g., pico cells, femto cells, etc.)having various shapes and small sizes are connected to a macro cellhaving a relatively large size. This aims to enable a user equipment(UE), which is an end user, to receive a high data rate to increasequality of experience in a state in which multilayered cells havingvertical layers, in which conventional macro cells are fundamentallyinvolved, are mixed.

However, in an environment in which a large number of small cells isarranged, a UE may be connected to two or more small cells to transmitand receive data. At this time, since the small cells are connected viaa non-ideal backhaul, it is difficult to share data or schedulinginformation. At this time, the UE shall transmit control information ofseveral small cells using a restricted uplink control channel.Accordingly, there is a need to transmit uplink control informationusing a method different from that of a legacy cellular system.

DISCLOSURE Technical Problem

The present invention devised to solve the problem relates to a methodfor controlling uplink transmit power (e.g., PUCCH and PUCCH transmitpower) in an environment, in which a user equipment (UE) is connected totwo or more small cells, and an apparatus supporting the same.

An object of the present invention devised to solve the problem lies inmethods for reporting power headroom of a UE.

Another object of the present invention devised to solve the problemlies in apparatuses supporting such methods.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

Technical Solution

The present invention provides methods for controlling transmit power inan environment supporting a multi-connectivity mode, in which a userequipment (UE) is connected to two or more small cells, and apparatusessupporting the same.

The object of the present invention can be achieved by providing amethod for controlling uplink transmit power of a user equipment (UE) ina radio access system supporting a multi-connectivity mode including theUE calculating physical uplink control channel (PUCCH) transmit powerfor two or more small cells in the multi-connectivity mode and the UEtransmitting respective PUCCH signals to the two or more small cellsbased on the PUCCH transmit power. At this time, in themulti-connectivity mode, the UE may maintain multiple connections withthe two or more small cells, and the two or more small cells may beconnected to each other via a non-ideal backhaul link.

The method may further include receiving two or more higher layersignals including first power parameters from the two or more smallcells, receiving two or more physical downlink control channel (PDCCH)signals including second power parameters from the two or more smallcells, and measuring path loss values of the two or more small cells. Atthis time, the PUCCH transmit power may be calculated based on the firstpower parameters, the second power parameters and the path loss values.

In another aspect of the present invention, provided herein is a userequipment (UE) for controlling uplink transmit power in a radio accesssystem supporting a multi-connectivity mode including a transmitter, areceiver, and a processor connected to the transmitter and the receiverto control the uplink transmit power. At this time, the processor may beconfigured to calculate physical uplink control channel (PUCCH) transmitpower for two or more small cells in the multi-connectivity mode andcontrol the transmitter to transmit respective PUCCH signals to the twoor more small cells based on the PUCCH transmit power. In themulti-connectivity mode, the UE may maintain multiple connections withthe two or more small cells, and the two or more small cells may beconnected to each other via a non-ideal backhaul link.

The processor may be configured to control the receiver to receive twoor more higher layer signals including first power parameters from thetwo or more small cells, control the receiver to receive two or morephysical downlink control channel (PDCCH) signals including second powerparameters from the two or more small cells, and measure path lossvalues of the two or more small cells. The PUCCH transmit power may becalculated based on the first power parameters, the second powerparameters and the path loss values.

The PUCCH transmit power may be calculated as shown in the followingequation.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min \begin{Bmatrix}{{P_{{CMAX},c}(i)},} \\\begin{matrix}{P_{{0{\_ PUCCH}},c} + {PL}_{c} + {h_{c}\left( {n_{CQI},n_{HARQ},n_{SR}} \right)} +} \\{{\Delta_{F\_ PUCCH}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g_{c}(i)}}\end{matrix}\end{Bmatrix}}} & \lbrack{Equation}\rbrack\end{matrix}$

where, P_(CMAX,c)(i) denotes maximum transmit power in a subframe i of asmall cell c, P₀ _(—) _(PUCCH,c) denotes a sum of P₀ _(—) _(NOMINAL)_(—) _(PUCCH,c) which is a cell-specific parameter set with respect tothe serving cell c at a higher layer and P₀ _(—) _(UE) _(—) _(PUCCH,c)which is a UE-specific parameter, h_(c)(n_(CQI),n_(HARQ),n_(SR)) denotesa parameter depending on a PUCCH format of the small cell c, n_(CQI),n_(HARQ), and n_(SR) respectively denoting channel status information(CQI) bit number, ACK/NACK information bit number, and schedulingrequest (SR) information bit number, Δ_(F) _(—) _(PUCCH) (F) denotes avalue set at the higher layer according to a PUCCH format, Δ_(TxD)(FT)denotes a value set at the higher layer to be used when the UE transmitsthe PUCCH signals via two antenna ports, g_(c)(i) denotes a valueacquired from a PUCCH power control command transmitted via a physicaldownlink control channel (PDCCH) signal, and c denotes an index of eachof the two or more small cells in the multi-connectivity mode.

At this time, P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) may be a value commonlyset with respect to the two or more small cells and P₀ _(—) _(UE) _(—)_(PUCCH,c) may be a value individually set with respect to the two ormore small cells.

Alternatively, P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) may be a valueindividually set with respect to the two or more small cells and P₀ _(—)_(UE) _(—) _(PUCCH,c) may be a value commonly set with respect to thetwo or more small cells.

The first power parameters may include at least one of P₀ _(—)_(NOMINAL) _(—) _(PUCCH,c), P₀ _(—) _(UE) _(—) _(PUCCH,c), Δ_(F) _(—)_(PUCCH)(F) and Δ_(TxD)(F′), and the second power parameters may includeg_(c)(i), δ_(PUCCH) and a parameter indicating a PUCCH format.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

As is apparent from the above description, the embodiments of thepresent invention have the following effects.

First, it is possible to efficiently save power in a multi-connectivitymode in which a user equipment (UE) is connected to two or more smallcells.

Second, a UE reports a power headroom value thereof to an eNB, such thatthe eNB can efficiently control transmit power of the UE.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 is a conceptual diagram illustrating physical channels used inthe embodiments and a signal transmission method using the physicalchannels.

FIG. 2 is a diagram illustrating a structure of a radio frame for use inthe embodiments.

FIG. 3 is a diagram illustrating an example of a resource grid of adownlink slot according to the embodiments.

FIG. 4 is a diagram illustrating a structure of an uplink subframeaccording to the embodiments.

FIG. 5 is a diagram illustrating a structure of a downlink subframeaccording to the embodiments.

FIG. 6 illustrates PUCCH formats 1a and 1b for use in a normal cyclicprefix (CP) case and FIG. 7 illustrates PUCCH formats 1a and 1b for usein an extended CP case.

FIG. 8 illustrates PUCCH formats 2/2a/2b in a normal cyclic prefix (CP)case, and FIG. 9 illustrates PUCCH formats 2/2a/2b in an extended CPcase.

FIG. 10 illustrates ACK/NACK channelization for PUCCH formats 1a and 1b.

FIG. 11 illustrates channelization for a hybrid structure of PUCCHformat 1a/1b and format 2/2a/2b in the same PRB.

FIG. 12 illustrates allocation of a physical resource block (PRB).

FIG. 13 is a diagram illustrating an example of a component carrier (CC)of the embodiments and carrier aggregation (CA) used in an LTE_A system.

FIG. 14 illustrates a subframe structure of an LTE-A system according tocross-carrier scheduling.

FIG. 15 is conceptual diagram illustrating a construction of servingcells according to cross-carrier scheduling.

FIG. 16 is a conceptual diagram illustrating CA PUCCH signal processing.

FIG. 17 is a diagram showing one method for calculating PUCCH transmitpower; and

FIG. 18 shows an apparatus for implementing the methods described withreference to FIGS. 1 to 17.

BEST MODE

The following embodiments of the present invention provide methods forcontrolling transmit power and transmitting channel status information(CSI) in an environment supporting a multi-connectivity mode, in which auser equipment (UE) is connected to two or more small cells, andapparatuses supporting the same.

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentinvention (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmitter is a fixed and/or mobile node that provides a data serviceor a voice service and a receiver is a fixed and/or mobile node thatreceives a data service or a voice service. Therefore, a UE may serve asa transmitter and a BS may serve as a receiver, on an UpLink (UL).Likewise, the UE may serve as a receiver and the BS may serve as atransmitter, on a DownLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3^(rd) Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, 3GPP TS 36.321 and 3GPP TS 36.331. That is, the steps or parts,which are not described to clearly reveal the technical idea of thepresent disclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the invention.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

For example, the term used in embodiments of the present disclosure, adata block is interchangeable with a transport block in the samemeaning. In addition, the MCS/TBS index table used in the LTE/LTE-Asystem can be defined as a first table or a legacy table, and theMCS/TBS index table which is used for supporting the 256QAM can bedefined as a second table or a new table.

The embodiments of the present disclosure can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

1.1 System Overview

FIG. 1 illustrates physical channels and a general method using thephysical channels, which may be used in embodiments of the presentdisclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB.

During the initial cell search, the UE may monitor a DL channel state byreceiving a Downlink Reference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present disclosure.

FIG. 2( a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (T_(f)=307200·T_(s)) long, includingequal-sized 20 slots indexed from 0 to 19. Each slot is 0.5 ms(T_(slot)=15360·T_(s)) long. One subframe includes two successive slots.An i^(th) subframe includes 2i^(th) and (2i+1)^(th) slots. That is, aradio frame includes 10 subframes. A time required for transmitting onesubframe is defined as a Transmission Time Interval (TTI). T_(s) is asampling time given as T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns).One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols or SC-FDMA symbols in the time domain by aplurality of Resource Blocks (RBs) in the frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2( b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(T_(f)=307200·T_(s)) long, including two half-frames each having alength of 5 ms (=153600·T_(s)) long. Each half-frame includes fivesubframes each being 1 ms (=30720·T_(s)) long. An i^(th) subframeincludes 2i^(th) and (2i+1)^(th) slots each having a length of 0.5 ms(T_(slot)=15360·T_(s)). T_(s) is a sampling time given as T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special subframe Normal cyclic Extended cyclicNormal cyclic Extended cyclic configuration DwPTS prefix in uplinkprefix in uplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, N_(DL)depends on a DL transmission bandwidth. A UL slot may have the samestructure as a DL slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe are allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a Physical Control FormatIndicator Channel (PCFICH), a PDCCH, and a Physical Hybrid ARQ IndicatorChannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

1.2 Physical Downlink Control Channel (PDCCH)

1.2.1 PDCCH Overview

The PDCCH may deliver information about resource allocation and atransport format for a Downlink Shared Channel (DL-SCH) (i.e. a DLgrant), information about resource allocation and a transport format foran Uplink Shared Channel (UL-SCH) (i.e. a UL grant), paging informationof a Paging Channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher-layer control message such as arandom access response transmitted on the PDSCH, a set of Tx powercontrol commands for individual UEs of a UE group, Voice Over InternetProtocol (VoIP) activation indication information, etc.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive Control Channel Elements (CCEs). A PDCCH made upof one or more consecutive CCEs may be transmitted in the control regionafter subblock interleaving. A CCE is a logical allocation unit used toprovide a PDCCH at a code rate based on the state of a radio channel. ACCE includes a plurality of RE Groups (REGs). The format of a PDCCH andthe number of available bits for the PDCCH are determined according tothe relationship between the number of CCEs and a code rate provided bythe CCEs.

1.2.2 PDCCH Structure

A plurality of PDCCHs for a plurality of UEs may be multiplexed andtransmitted in the control region. A PDCCH is made up of an aggregate ofone or more consecutive CCEs. A CCE is a unit of 9 REGs each REGincluding 4 REs. Four Quadrature Phase Shift Keying (QPSK) symbols aremapped to each REG. REs occupied by RSs are excluded from REGs. That is,the total number of REGs in an OFDM symbol may be changed depending onthe presence or absence of a cell-specific RS. The concept of an REG towhich four REs are mapped is also applicable to other DL controlchannels (e.g. the PCFICH or the PHICH). Let the number of REGs that arenot allocated to the PCFICH or the PHICH be denoted by N_(REG). Then thenumber of CCEs available to the system is N_(CCE) (=└N_(REG)/9┘) and theCCEs are indexed from 0 to N_(CCE)−1.

To simplify the decoding process of a UE, a PDCCH format including nCCEs may start with a CCE having an index equal to a multiple of n. Thatis, given CCE i, the PDCCH format may start with a CCE satisfying i modn=0

The eNB may configure a PDCCH with 1, 2, 4, or 8 CCEs. {1, 2, 4, 8} arecalled CCE aggregation levels. The number of CCEs used for transmissionof a PDCCH is determined according to a channel state by the eNB. Forexample, one CCE is sufficient for a PDCCH directed to a UE in a good DLchannel state (a UE near to the eNB). On the other hand, 8 CCEs may berequired for a PDCCH directed to a UE in a poor DL channel state (a UEat a cell edge) in order to ensure sufficient robustness.

[Table 2] below illustrates PDCCH formats. 4 PDCCH formats are supportedaccording to CCE aggregation levels as illustrated in [Table 2].

TABLE 2 Number of Number of Number of PDCCH format CCEs (n) REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

A different CCE aggregation level is allocated to each UE because theformat or Modulation and Coding Scheme (MCS) level of controlinformation delivered in a PDCCH for the UE is different. An MCS leveldefines a code rate used for data coding and a modulation order. Anadaptive MCS level is used for link adaptation. In general, three orfour MCS levels may be considered for control channels carrying controlinformation.

Regarding the formats of control information, control informationtransmitted on a PDCCH is called DCI. The configuration of informationin PDCCH payload may be changed depending on the DCI format. The PDCCHpayload is information bits. [Table 3] lists DCI according to DCIformats.

TABLE 3 DCI Format Description Format 0 Resource grants for the PUSCHtransmissions (uplink) Format 1 Resource assignments for single codewordPDSCH transmissions (transmission modes 1, 2 and 7) Format 1A Compactsignaling of resource assignments for single codeword PDSCH (all modes)Format 1B Compact resource assignments for PDSCH using rank-1 closedloop precoding (mode 6) Format 1C Very compact resource assignments forPDSCH (e.g. paging/broadcast system information) Format 1D Compactresource assignments for PDSCH using multi-user MIMO (mode 5) Format 2Resource assignments for PDSCH for closed-loop MIMO operation (mode 4)Format 2A Resource assignments for PDSCH for open-loop MIMO operation(mode 3) Format Power control commands for PUCCH and PUSCH with 3/3A2-bit/1-bit power adjustment Format 4 Scheduling of PUSCH in one UL cellwith multi-antenna port transmission mode

Referring to [Table 3], the DCI formats include Format 0 for PUSCHscheduling, Format 1 for single-codeword PDSCH scheduling, Format 1A forcompact single-codeword PDSCH scheduling, Format 1C for very compactDL-SCH scheduling, Format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, Format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, and Format 3/3A for transmission ofTransmission Power Control (TPC) commands for uplink channels. DCIFormat 1A is available for PDSCH scheduling irrespective of thetransmission mode of a UE.

The length of PDCCH payload may vary with DCI formats. In addition, thetype and length of PDCCH payload may be changed depending on compact ornon-compact scheduling or the transmission mode of a UE.

The transmission mode of a UE may be configured for DL data reception ona PDSCH at the UE. For example, DL data carried on a PDSCH includesscheduled data, a paging message, a random access response, broadcastinformation on a BCCH, etc. for a UE. The DL data of the PDSCH isrelated to a DCI format signaled through a PDCCH. The transmission modemay be configured semi-statically for the UE by higher-layer signaling(e.g. Radio Resource Control (RRC) signaling). The transmission mode maybe classified as single antenna transmission or multi-antennatransmission.

A transmission mode is configured for a UE semi-statically byhigher-layer signaling. For example, multi-antenna transmission schememay include transmit diversity, open-loop or closed-loop spatialmultiplexing, Multi-User Multiple Input Multiple Output (MU-MIMO), orbeamforming. Transmit diversity increases transmission reliability bytransmitting the same data through multiple Tx antennas. Spatialmultiplexing enables high-speed data transmission without increasing asystem bandwidth by simultaneously transmitting different data throughmultiple Tx antennas. Beamforming is a technique of increasing theSignal to Interference plus Noise Ratio (SINR) of a signal by weightingmultiple antennas according to channel states.

A DCI format for a UE depends on the transmission mode of the UE. The UEhas a reference DCI format monitored according to the transmission modeconfigure for the UE. The following 10 transmission modes are availableto UEs:

(1) Transmission mode 1: Single antenna port (port 0);

(2) Transmission mode 2: Transmit diversity;

(3) Transmission mode 3: Open-loop spatial multiplexing when the numberof layer is larger than 1 or Transmit diversity when the rank is 1;

(4) Transmission mode 4: Closed-loop spatial multiplexing;

(5) Transmission mode 5: MU-MIMO;

(6) Transmission mode 6: Closed-loop rank-1 precoding;

(7) Transmission mode 7: Precoding supporting a single layertransmission, which does not based on a codebook (Rel-8);

(8) Transmission mode 8: Precoding supporting up to two layers, which donot based on a codebook (Rel-9);

(9) Transmission mode 9: Precoding supporting up to eight layers, whichdo not based on a codebook (Rel-10); and

(10) Transmission mode 10: Precoding supporting up to eight layers,which do not based on a codebook, used for CoMP (Rel-11).

1.2.3 PDCCH Transmission

The eNB determines a PDCCH format according to DCI that will betransmitted to the UE and adds a Cyclic Redundancy Check (CRC) to thecontrol information. The CRC is masked by a unique Identifier (ID) (e.g.a Radio Network Temporary Identifier (RNTI)) according to the owner orusage of the PDCCH. If the PDCCH is destined for a specific UE, the CRCmay be masked by a unique ID (e.g. a cell-RNTI (C-RNTI)) of the UE. Ifthe PDCCH carries a paging message, the CRC of the PDCCH may be maskedby a paging indicator ID (e.g. a Paging-RNTI (P-RNTI)). If the PDCCHcarries system information, particularly, a System Information Block(SIB), its CRC may be masked by a system information ID (e.g. a SystemInformation RNTI (SI-RNTI)). To indicate that the PDCCH carries a randomaccess response to a random access preamble transmitted by a UE, its CRCmay be masked by a Random Access-RNTI (RA-RNTI).

Then the eNB generates coded data by channel-encoding the CRC-addedcontrol information. The channel coding may be performed at a code ratecorresponding to an MCS level. The eNB rate-matches the coded dataaccording to a CCE aggregation level allocated to a PDCCH format andgenerates modulation symbols by modulating the coded data. Herein, amodulation order corresponding to the MCS level may be used for themodulation. The CCE aggregation level for the modulation symbols of aPDCCH may be one of 1, 2, 4, and 8. Subsequently, the eNB maps themodulation symbols to physical REs (i.e. CCE to RE mapping).

1.2.4 Blind Decoding (BD)

A plurality of PDCCHs may be transmitted in a subframe. That is, thecontrol region of a subframe includes a plurality of CCEs, CCE 0 to CCEN_(CCE,k)−1. N_(CCE,k) is the total number of CCEs in the control regionof a k^(th) subframe. A UE monitors a plurality of PDCCHs in everysubframe. This means that the UE attempts to decode each PDCCH accordingto a monitored PDCCH format.

The eNB does not provide the UE with information about the position of aPDCCH directed to the UE in an allocated control region of a subframe.Without knowledge of the position, CCE aggregation level, or DCI formatof its PDCCH, the UE searches for its PDCCH by monitoring a set of PDCCHcandidates in the subframe in order to receive a control channel fromthe eNB. This is called blind decoding. Blind decoding is the process ofdemasking a CRC part with a UE ID, checking a CRC error, and determiningwhether a corresponding PDCCH is a control channel directed to a UE bythe UE.

The UE monitors a PDCCH in every subframe to receive data transmitted tothe UE in an active mode. In a Discontinuous Reception (DRX) mode, theUE wakes up in a monitoring interval of every DRX cycle and monitors aPDCCH in a subframe corresponding to the monitoring interval. ThePDCCH-monitored subframe is called a non-DRX subframe.

To receive its PDCCH, the UE should blind-decode all CCEs of the controlregion of the non-DRX subframe. Without knowledge of a transmitted PDCCHformat, the UE should decode all PDCCHs with all possible CCEaggregation levels until the UE succeeds in blind-decoding a PDCCH inevery non-DRX subframe. Since the UE does not know the number of CCEsused for its PDCCH, the UE should attempt detection with all possibleCCE aggregation levels until the UE succeeds in blind decoding of aPDCCH.

In the LTE system, the concept of Search Space (SS) is defined for blinddecoding of a UE. An SS is a set of PDCCH candidates that a UE willmonitor. The SS may have a different size for each PDCCH format. Thereare two types of SSs, Common Search Space (CSS) andUE-specific/Dedicated Search Space (USS).

While all UEs may know the size of a CSS, a USS may be configured foreach individual UE. Accordingly, a UE should monitor both a CSS and aUSS to decode a PDCCH. As a consequence, the UE performs up to 44 blinddecodings in one subframe, except for blind decodings based on differentCRC values (e.g., C-RNTI, P-RNTI, SI-RNTI, and RA-RNTI).

In view of the constraints of an SS, the eNB may not secure CCEresources to transmit PDCCHs to all intended UEs in a given subframe.This situation occurs because the remaining resources except forallocated CCEs may not be included in an SS for a specific UE. Tominimize this obstacle that may continue in the next subframe, aUE-specific hopping sequence may apply to the starting point of a USS.

[Table 4] illustrates the sizes of CSSs and USSs.

TABLE 4 Number of Number of candidates candidates Number of CCEs incommon in dedicated PDCCH format (n) search space search space 0 1 — 6 12 — 6 2 4 4 2 3 8 2 2

To mitigate the load of the UE caused by the number of blind decodingattempts, the UE does not search for all defined DCI formatssimultaneously. Specifically, the UE always searches for DCI Format 0and DCI Format 1A in a USS. Although DCI Format 0 and DCI Format 1A areof the same size, the UE may distinguish the DCI formats by a flag forformat0/format 1 a differentiation included in a PDCCH. Other DCIformats than DCI Format 0 and DCI Format 1A, such as DCI Format 1, DCIFormat 1B, and DCI Format 2 may be required for the UE.

The UE may search for DCI Format 1A and DCI Format 1C in a CSS. The UEmay also be configured to search for DCI Format 3 or 3A in the CSS.Although DCI Format 3 and DCI Format 3A have the same size as DCI Format0 and DCI Format 1A, the UE may distinguish the DCI formats by a CRCscrambled with an ID other than a UE-specific ID.

An SS S_(k) ^((L)) is a PDCCH candidate set with a CCE aggregation levelLε{1,2,4,8}. The CCEs of PDCCH candidate set m in the SS may bedetermined by the following equation.

L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  [Equation 1]

where M^((L)) is the number of PDCCH candidates with CCE aggregationlevel L to be monitored in the SS, m=0, . . . , M^((L))−1, i is theindex of a CCE in each PDCCH candidate, and i=0, . . . , L−1.k=└n_(s)/2┘ where is the index of a slot in a radio frame.

As described before, the UE monitors both the USS and the CSS to decodea PDCCH. The CSS supports PDCCHs with CCE aggregation levels {4, 8} andthe USS supports PDCCHs with CCE aggregation levels {1, 2, 4, 8}. [Table5] illustrates PDCCH candidates monitored by a UE.

TABLE 5 Search space S_(k) ^((L)) Number of PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE- 1 6 6 specific 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

Referring to [Equation 1], for two aggregation levels, L=4 and L=8,Y_(k) is set to 0 in the CSS, whereas Y_(k) is defined by [Equation 2]for aggregation level L in the USS.

Y _(k)=(A·Y _(k-1))mod D  [Equation 2]

where Y⁻¹=n_(RNTI)≠0, n_(RNTI) indicating an RNTI value. A=39827 andD=65537.

1.3. PUCCH (Physical Uplink Control Channel)

PUCCH may include the following formats to transmit control information.

(1) Format 1: On-Off keying (OOK) modulation, used for SR (SchedulingRequest)

(2) Format 1a & 1b: Used for ACK/NACK transmission

-   -   1) Format 1a: BPSK ACK/NACK for 1 codeword        -   2) Format 1b: QPSK ACK/NACK for 2 codewords

(3) Format 2: QPSK modulation, used for CQI transmission

(4) Format 2a & Format 2b: Used for simultaneous transmission of CQI andACK/NACK

(5) Format 3: Used for multiple ACK/NACK transmission in a carrieraggregation environment

Table 6 shows a modulation scheme according to PUCCH format and thenumber of bits per subframe. Table 7 shows the number of referencesignals (RS) per slot according to PUCCH format. Table 8 shows SC-FDMAsymbol location of RS (reference signal) according to PUCCH format. InTable 6, PUCCH format 2a and PUCCH format 2b correspond to a case ofnormal cyclic prefix (CP).

TABLE 6 PUCCH No. of bits per format Modulation scheme subframe, Mbit 1N/A N/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2b QPSK + BPSK22 3 QPSK 48

TABLE 7 PUCCH format Normal CP Extended CP 1, 1a, 1b 3 2 2, 3 2 1 2a, 2b2 N/A

TABLE 8 SC-FDMA symbol location of RS PUCCH format Normal CP Extended CP1, 1a, 1b 2, 3, 4 2, 3 2, 3 1, 5 3 2a, 2b 1, 5 N/A

FIG. 6 shows PUCCH formats 1a and 1b in case of a normal cyclic prefix.And, FIG. 7 shows PUCCH formats 1a and 1b in case of an extended cyclicprefix.

According to the PUCCH formats 1a and 1b, control information of thesame content is repeated in a subframe by slot unit. In each userequipment, ACK/NACK signal is transmitted on a different resourceconstructed with a different cyclic shift (CS) (frequency domain code)and an orthogonal cover (OC) or orthogonal cover code (OCC) (time domainspreading code) of CG-CAZAC (computer-generated constant amplitude zeroauto correlation) sequence. For instance, the OC includes Walsh/DFTorthogonal code. If the number of CS and the number of OC are 6 and 3,respectively, total 18 user equipments may be multiplexed within thesame PRB (physical resource block) with reference to a single antenna.Orthogonal sequences w0, w1, w2 and w3 may be applicable to a randomtime domain (after FFT modulation) or a random frequency domain (beforeFFT modulation).

For persistent scheduling with SR, ACK/NACK resource constructed withCS, OC and PRB (physical resource block) may be allocated to a userequipment through RRC (radio resource control. For non-persistentscheduling with dynamic ACK/NACK, the ACK/NACK resource may beimplicitly allocated to a user equipment using a smallest CCE index ofPDCCH corresponding to PDSCH.

Length-4 orthogonal sequence (OC) and length-3 orthogonal sequence forPUCCH format 1/1a/1b are shown in Table 9 and Table 10, respectively.

TABLE 9 Orthogonal sequences Sequence index n_(oc) (n_(s)) [w(0) . . .w(N_(SF) ^(PUCCH) − 1)] 0 [+1 +1 +1 +1] 1 [+1 −1 +1 −1] 2 [+1 −1 −1 +1]

TABLE 10 Orthogonal sequences Sequence index n_(oc) (n_(s)) [w(0) . . .w(N_(SF) ^(PUCCH) − 1)] 0 [1 1 1] 1 [1 e^(j2π/3) e^(j4π/3)] 2 [1e^(j4π/3) e^(j2π/3)]

Orthogonal sequence (OC)) [ w(0) . . . w(N_(RS) ^(PUCCH)−1))] for areference signal in PUCCH format 1/1a/1b is shown in Table 11.

TABLE 11 Sequence index n _(oc) (n_(s)) Normal cyclic prefix Extendedcyclic prefix 0 [1 1 1] [1 1] 1 [1 e^(j2π/3) e^(j4π/3)] [1 −1] 2 [1e^(j4π/3) e^(j2π/3)] N/A

FIG. 8 shows PUCCH format 2/2a/2b in case of a normal cyclic prefix.And, FIG. 9 shows PUCCH format 2/2a/2b in case of an extended cyclicprefix.

Referring to FIG. 8 and FIG. 9, in case of a normal CP, a subframe isconstructed with 10 QPSK data symbols as well as RS symbol. Each QPSKsymbol is spread in a frequency domain by CS and is then mapped to acorresponding SC-FDMA symbol. SC-FDMA symbol level CS hopping may beapplied to randomize inter-cell interference. The RS may be multiplexedby CDM using a cyclic shift. For instance, assuming that the number ofavailable CSs is 12, 12 user equipments may be multiplexed in the samePRB. For instance, assuming that the number of available CSs is 6, 6user equipments may be multiplexed in the same PRB. In brief, aplurality of user equipments in PUCCH format 1/1a/1b and PUCCH format2/2a/2b may be multiplexed by ‘CS+OC+PRB’ and ‘ CS+PRB’, respectively.

FIG. 10 is a diagram of ACK/NACK channelization for PUCCH formats 1a and1b. In particular, FIG. 10 corresponds to a case of ‘Δ_(shift)^(PUCCH)=2’

FIG. 11 is a diagram of channelization for a hybrid structure of PUCCHformat 1/1a/1b and PUCCH format 2/2a/2b.

Cyclic shift (CS) hopping and orthogonal cover (OC) remapping may beapplicable in a following manner.

(1) Symbol-based cell-specific CS hopping for randomization ofinter-cell interference

(2) Slot level CS/OC remapping

-   -   1) For inter-cell interference randomization    -   2) Slot based access for mapping between ACK/NACK channel and        resource (k)

Meanwhile, resource n_(r) for PUCCH format 1/1a/1b may include thefollowing combinations.

(1) CS (=equal to DFT orthogonal code at symbol level) (n_(cs))

(2) OC (orthogonal cover at slot level) (n_(oc))

(3) Frequency RB (Resource Block) (n_(rb))

If indexes indicating CS, OC and RB are set to n_(cs), n_(oc), n_(rb),respectively, a representative index n_(r) may include n_(cs), n_(oc)and n_(rb). In this case, the n_(r) may meet the condition of‘n_(r)=(n_(cs), n_(oc), n_(rb))’.

The combination of CQI, PMI, RI, CQI and ACK/NACK may be deliveredthrough the PUCCH format 2/2a/2b. And, Reed Muller (RM) channel codingmay be applicable.

For instance, channel coding for UL (uplink) CQI in LTE system may bedescribed as follows. First of all, bitstreams a₀, a₁, a₂, a₃, . . .a_(A-1) may be coded using (20, A) RM code. In this case, a₀ and a_(A-1)indicates MSB (Most Significant Bit) and LSB (Least Significant Bit),respectively. In case of an extended cyclic prefix, maximum informationbits include 11 bits except a case that QI and ACK/NACK aresimultaneously transmitted. After coding has been performed with 20 bitsusing the RM code, QPSK modulation may be applied. Before the BPSKmodulation, coded bits may be scrambled.

Table 12 shows a basic sequence for (20, A) code.

TABLE 12 i M_(i, 0) M_(i, 1) M_(i, 2) M_(i, 3) M_(i, 4) M_(i, 5)M_(i, 6) M_(i, 7) M_(i, 8) M_(i, 9) M_(i, 10) M_(i, 11) M_(i, 12) 0 1 10 0 0 0 0 0 0 0 1 1 0 1 1 1 1 0 0 0 0 0 0 1 1 1 0 2 1 0 0 1 0 0 1 0 1 11 1 1 3 1 0 1 1 0 0 0 0 1 0 1 1 1 4 1 1 1 1 0 0 0 1 0 0 1 1 1 5 1 1 0 01 0 1 1 1 0 1 1 1 6 1 0 1 0 1 0 1 0 1 1 1 1 1 7 1 0 0 1 1 0 0 1 1 0 1 11 8 1 1 0 1 1 0 0 1 0 1 1 1 1 9 1 0 1 1 1 0 1 0 0 1 1 1 1 10 1 0 1 0 0 11 1 0 1 1 1 1 11 1 1 1 0 0 1 1 0 1 0 1 1 1 12 1 0 0 1 0 1 0 1 1 1 1 1 113 1 1 0 1 0 1 0 1 0 1 1 1 1 14 1 0 0 0 1 1 0 1 0 0 1 0 1 15 1 1 0 0 1 11 1 0 1 1 0 1 16 1 1 1 0 1 1 1 0 0 1 0 1 1 17 1 0 0 1 1 1 0 0 1 0 0 1 118 1 1 0 1 1 1 1 1 0 0 0 0 0 19 1 0 0 0 0 1 1 0 0 0 0 0 0

Channel coding bits b₀, b₁, b₂, b₃, . . . , b_(B-1) may be generated byFormula 1.

$\begin{matrix}{b_{i} = {\sum\limits_{n = 0}^{A - 1}\; {\left( {a_{n} \cdot M_{i,n}} \right){mod}\mspace{14mu} 2}}} & \left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In Formula 3, ‘i=0, 1, 2, . . . , B−1’ is met.

In case of wideband repots, a bandwidth of UCI (uplink controlinformation) field for CQI/PMI can be represented as Tables 8 to 10 inthe following.

Table 13 shows UCI (Uplink Control Information) field for broadbandreport (single antenna port, transmit diversity) or open loop spatialmultiplexing PDSCH CQI feedback.

TABLE 13 Field Bandwidth Broadband CQI 4

Table 14 shows UL control information (UCI) field for CQI and PMIfeedback in case of wideband reports (closed loop spatial multiplexingPDSCH transmission).

TABLE 14 Bandwidth 2 antenna ports 4 antenna ports Field rank = 1 rank =2 rank = 1 Rank > 1 Wideband CQI 4 4 4 4 Spatial differential CQI 0 3 03 Precoding Matrix 2 1 4 4 Indication

Table 15 shows UL control information (UCI) field for RI feedback incase of wideband reports.

TABLE 15 Bit widths 4 antenna ports Field 2 antenna ports Max. 2 layersMax. 4 layers Rank Indication 1 1 2

FIG. 12 is a diagram for PRB allocation. Referring to FIG. 20, PRB maybe usable for PUCCH transmission in a slot n_(s).

2. Carrier Aggregation (CA) Environment

2.1 CA Overview

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘ cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguration message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 13 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure.

FIG. 13( a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 13( b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 13( b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≦N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≦M≦N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher-layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

2.2 Cross Carrier Scheduling

Two scheduling schemes, self-scheduling and cross carrier scheduling aredefined for a CA system, from the perspective of carriers or servingcells. Cross carrier scheduling may be called cross CC scheduling orcross cell scheduling.

In self-scheduling, a PDCCH (carrying a DL grant) and a PDSCH aretransmitted in the same DL CC or a PUSCH is transmitted in a UL CClinked to a DL CC in which a PDCCH (carrying a UL grant) is received.

In cross carrier scheduling, a PDCCH (carrying a DL grant) and a PDSCHare transmitted in different DL CCs or a PUSCH is transmitted in a UL CCother than a UL CC linked to a DL CC in which a PDCCH (carrying a ULgrant) is received.

Cross carrier scheduling may be activated or deactivated UE-specificallyand indicated to each UE semi-statically by higher-layer signaling (e.g.RRC signaling).

If cross carrier scheduling is activated, a Carrier Indicator Field(CIF) is required in a PDCCH to indicate a DL/UL CC in which aPDSCH/PUSCH indicated by the PDCCH is to be transmitted. For example,the PDCCH may allocate PDSCH resources or PUSCH resources to one of aplurality of CCs by the CIF. That is, when a PDCCH of a DL CC allocatesPDSCH or PUSCH resources to one of aggregated DL/UL CCs, a CIF is set inthe PDCCH. In this case, the DCI formats of LTE Release-8 may beextended according to the CIF. The CIF may be fixed to three bits andthe position of the CIF may be fixed irrespective of a DCI format size.In addition, the LTE Release-8 PDCCH structure (the same coding andresource mapping based on the same CCEs) may be reused.

On the other hand, if a PDCCH transmitted in a DL CC allocates PDSCHresources of the same DL CC or allocates PUSCH resources in a single ULCC linked to the DL CC, a CIF is not set in the PDCCH. In this case, theLTE Release-8 PDCCH structure (the same coding and resource mappingbased on the same CCEs) may be used.

If cross carrier scheduling is available, a UE needs to monitor aplurality of PDCCHs for DCI in the control region of a monitoring CCaccording to the transmission mode and/or bandwidth of each CC.Accordingly, an appropriate SS configuration and PDCCH monitoring areneeded for the purpose.

In the CA system, a UE DL CC set is a set of DL CCs scheduled for a UEto receive a PDSCH, and a UE UL CC set is a set of UL CCs scheduled fora UE to transmit a PUSCH. A PDCCH monitoring set is a set of one or moreDL CCs in which a PDCCH is monitored. The PDCCH monitoring set may beidentical to the UE DL CC set or may be a subset of the UE DL CC set.The PDCCH monitoring set may include at least one of the DL CCs of theUE DL CC set. Or the PDCCH monitoring set may be defined irrespective ofthe UE DL CC set. DL CCs included in the PDCCH monitoring set may beconfigured to always enable self-scheduling for UL CCs linked to the DLCCs. The UE DL CC set, the UE UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

If cross carrier scheduling is deactivated, this implies that the PDCCHmonitoring set is always identical to the UE DL CC set. In this case,there is no need for signaling the PDCCH monitoring set. However, ifcross carrier scheduling is activated, the PDCCH monitoring set may bedefined within the UE DL CC set. That is, the eNB transmits a PDCCH onlyin the PDCCH monitoring set to schedule a PDSCH or PUSCH for the UE.

FIG. 14 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present disclosure.

Referring to FIG. 14, three DL CCs are aggregated for a DL subframe forLTE-A UEs. DL CC ‘A’ is configured as a PDCCH monitoring DL CC. If a CIFis not used, each DL CC may deliver a PDCCH that schedules a PDSCH inthe same DL CC without a CIF. On the other hand, if the CIF is used byhigher-layer signaling, only DL CC ‘A’ may carry a PDCCH that schedulesa PDSCH in the same DL CC ‘ A’ or another CC. Herein, no PDCCH istransmitted in DL CC ‘B’ and DL CC C that are not configured as PDCCHmonitoring DL CCs.

FIG. 15 is conceptual diagram illustrating a construction of servingcells according to cross-carrier scheduling.

Referring to FIG. 15, an eNB (or BS) and/or UEs for use in a radioaccess system supporting carrier aggregation (CA) may include one ormore serving cells. In FIG. 8, the eNB can support a total of fourserving cells (cells A, B, C and D). It is assumed that UE A may includeCells (A, B, C), UE B may include Cells (B, C, D), and UE C may includeCell B. In this case, at least one of cells of each UE may be composedof P Cell. In this case, P Cell is always activated, and S Cell may beactivated or deactivated by the eNB and/or UE.

The cells shown in FIG. 15 may be configured per UE. The above-mentionedcells selected from among cells of the eNB, cell addition may be appliedto carrier aggregation (CA) on the basis of a measurement report messagereceived from the UE. The configured cell may reserve resources forACK/NACK message transmission in association with PDSCH signaltransmission. The activated cell is configured to actually transmit aPDSCH signal and/or a PUSCH signal from among the configured cells, andis configured to transmit CSI reporting and Sounding Reference Signal(SRS) transmission. The deactivated cell is configured not totransmit/receive PDSCH/PUSCH signals by an eNB command or a timeroperation, and CRS reporting and SRS transmission are interrupted.

2.3 CA PUCCH (Carrier Aggregation Physical Uplink Control Channel)

In a wireless communication system supportive of carrier aggregation,PUCCH format for feeding back UCI (e.g., multi-ACK/NACK bit) can bedefined. For clarity of the following description, such PUCCH formatshall be named CA PUCCH format.

FIG. 16 is a diagram for one example of a signal processing process ofCA PUCCH.

Referring to FIG. 16, a channel coding block generates coding bits(e.g., encoded bits, coded bits, etc.) (or codeword) b_0, b_1, . . . andb_N−1 by channel-coding information bits a_0, a_1, . . . and a_M−1(e.g., multiple ACK/NACK bits). In this case, the M indicates a size ofinformation bits and the N indicates a size of the coding bits. Theinformation bits may include multiple ACK/NACK for UL controlinformation (UCI), e.g., a plurality of data (or PDSCH) received via aplurality of DL CCS. In this case, the information bits a_0, a_1, . . .a_M−1 may be joint-coded irrespective of type/number/size of the UCIconfiguring the information bits. For instance, in case that informationbits include multiple ACK/NACK for a plurality of DL CCs, channel codingmay not be performed per DL CC or individual ACK/NACK bit but may beperformed on all bit information, from which a single codeword may begenerated. And, channel coding is non-limited by this. Moreover, thechannel coding may include one of simplex repetition, simplex coding, RM(Reed Muller) coding, punctured RM coding, TBCC (tail-bitingconvolutional coding), LDPC (low-density parity-check), turbo coding andthe like. Besides, coding bits may be rate-matched in consideration of amodulation order and a resource size (not shown in the drawing). A ratematching function may be included as a part of the channel coding blockor may be performed via a separate function block.

A modulator generates modulated symbols c_0, c_1 . . . c_L−1 bymodulating coding bits b_0, b_1 . . . b_N−1. In this case, the Lindicates a size of modulated symbol. This modulation scheme may beperformed in a manner of modifying a size and phase of a transmissionsignal. For instance, the modulation scheme may include one of n-PSK(Phase Shift Keying), n-QAM (Quadrature Amplitude Modulation) and thelike, where n is an integer equal to or greater than 2. In particular,the modulation scheme may include one of BPSK (Binary PSK), QPSK(Quadrature PSK), 8-PSK, QAM, 16-QAM, 64-QAM and the like.

A divider divides the modulated symbols c_0, c_1 . . . c_L−1 to slots,respectively. A sequence/pattern/scheme for dividing the modulatedsymbols to the slots may be specially non-limited. For instance, thedivider may be able to divide the modulated symbols to the correspondingslots in order from a head to tail (Localized scheme). In doing so, asshown in the drawing, the modulated symbols c_0, c_1 . . . c_L/2−1 maybe divided to the slot 0 and the modulated symbols c_(—) L/2, c_L/2+1 .. . c_L−1 may be divided to the slot 1. Moreover, the modulated symbolsmay be divided to the corresponding slots, respectively, by interleavingor permutation. For instance, the even-numbered modulated symbol may bedivided to the slot 0, while the odd-numbered modulated symbol may bedivided to the slot 1. The modulation scheme and the dividing scheme maybe switched to each other in order.

A DFT precoder may perform DFT precoding (e.g., 12-point DFT) on themodulated symbols divided to the corresponding slots to generate asingle carrier waveform. Referring to the drawing, the modulated symbolsc_0, c_1 . . . c_L/2−1 divided to the corresponding slot 0 may beDFT-precoded into DFT symbols d_0, d_1 . . . d_L/2−1, and the modulatedsymbols c_(—) L/2, c_L/2+1 . . . c_L−1 divided to the slot 1 may beDFT-precoded into DFT symbols d_(—) L/2, d_(—) L/2+1 . . . d_L−1.Moreover, the DFT precoding may be replaced by another linear operation(e.g., Walsh precoding) corresponding thereto.

A spreading block may spread the DFT-performed signal at SC-FDMA symbolslevel (e.g., time domain). The time-domain spreading at the SC-FDMAlevel may be performed using a spreading code (sequence). The spreadingcode may include pseudo orthogonal code and orthogonal code. The pseudoorthogonal code may include PN (pseudo noise) code, by which the pseudoorthogonal code may be non-limited. The orthogonal code may includeWalsh code and DFT code, by which the orthogonal code may benon-limited. The orthogonal code (OC) may be interchangeably used withone of an orthogonal sequence, an orthogonal cover (OC) and anorthogonal cover code (OCC). In this specification, for example, theorthogonal code may be mainly described as a representative example ofthe spreading code for clarity and convenience of the followingdescription. Optionally, the orthogonal code may be substituted with thepseudo orthogonal code. A maximum value of a spreading code size (or aspreading factor: SF) may be limited by the number of SC-FDAM symbolsused for control information transmission. For example, in case that 5SC-FDMA symbols are used in one slot for control informationtransmission, orthogonal codes (or pseudo orthogonal codes) w0, w1, w2,w3 and w4 of length 5 may be used per slot. The SF may mean a spreadingdegree of the control information and may be associated with amultiplexing order or an antenna multiplexing order of a user equipment.The SF may be variable like 1, 2, 3, 4, 5 . . . depending on arequirement of a system. The SF may be defined in advance between a basestation and a user equipment. And, the SF may be notified to a userequipment via DCI or RRC signaling.

The signal generated through the above-described process may be mappedto subcarrier within the PRB and may be then transformed into atime-domain signal through IFFT. CP may be attached to the time-domainsignal. The generated SC-FDMA symbol may be then transmitted through anRF stage.

3. CSI Reporting Method in Small Cell Environment

3.1 Small Cell Environment

The term “cell” described in the embodiments of the present inventionmay fundamentally include downlink resources and optionally includeuplink resources (see Chapter 2.1). At this time, linkage betweencarrier frequency for downlink resources and carrier frequency foruplink resources is specified in system information (SI) delivered viadownlink resources.

In addition, the term “cell” means a specific frequency region or aspecific geographical region as coverage of an eNB. The term “cell mayhave the same meaning as the eNB supporting specific coverage, forconvenience of description. For example, a macro eNB and a macro cellmay be used as the same meaning and a small base station and a smallcell may be used as the same meaning. The terms cell and base stationmay have respective original meanings upon being explicitlydistinguished.

In a next-generation wireless communication system, in order to morestably secure a data service such as multimedia, interest inintroduction of a hierarchical cell structure in which a micro cell, apico cell and/or a femto cell, all of which are small cells forlow-power/short-range communication, are mixed or a heterogeneous cellstructure to a homogeneous network based on a macro cell has increased.This is because additional installation of a macro cell in an existingeNB can improve system performance but is not efficient in terms of costand complexity.

Assume that the term “cell” applied to the following embodiments refersto a small cell unless stated otherwise. However, the present inventionis applicable to a cell (e.g., a macro cell) used in a general cellularsystem.

In addition, the technologies described in Chapters 1 to 3 areapplicable to the following embodiments of the present invention.

3.2 Multi-Connectivity Mode

In the embodiments of the present invention, a new connectivity mode isproposed. That is, a multi-connectivity mode in which a UE issimultaneously connected to two or more cells is proposed. The UE may besimultaneously connected to a plurality of cells having the samedownlink carrier frequency or different downlink carrier frequencies inthe multi-connectivity mode. The multi-connectivity mode may be referredto as a multi-connection mode, a new connectivity mode or a newconnection mode as the connection mode newly proposed in the embodimentsof the present invention.

The multi-connectivity mode means that the UE may be simultaneouslyconnected to a plurality of cells. Hereinafter, for convenience ofdescription, assume that the UE is connected to two cells. The presentinvention is equally applicable to the case in which the UE is connectedto three or more cells.

For example, the UE may simultaneously receive services from a firstcell and a second cell. At this time, the UE may receive functionalities(e.g., connection management, mobility management) provided by a controlplane (C-plane) via the first cell and the second cell.

In addition, the UE may perform carrier aggregation (CA) with two ormore cells. For example, the first cell may use n (n being an arbitrarypositive integer) arbitrary carriers and the second cell may use k (kbeing an arbitrary positive integer) arbitrary carriers. At this time,the carriers of the first cell and the second cell are the samefrequency carriers or different frequency carriers. For example, thefirst cell may use F1 and F2 frequency bands and the second cell may useF2 and F3 frequency bands.

A plurality of cells may physically exist in the same position ordifferent positions. At this time, assume that the plurality of cells isconnected to each other via a backhaul but the backhaul is a non-idealbackhaul via which it is difficult to share scheduling information ordata of a specific UE due to very large transmission delay.

In the embodiments of the present invention, assume that the cell is asmall cell. For example, as an environment in which the small cell isarranged, a hot spot of a city may be considered. That is, since aplurality of small cells is arranged in a specific region, assume that adifference in timing advance (TA) value between small cells, to whichthe UE is simultaneously connected, is small. That is, under a specificcondition, several small cells may simultaneously receive the signaltransmitted by the UE.

In the multi-connectivity mode, the UE may receive synchronizationsignals from a plurality of small cells and maintain downlinksynchronization. In addition, the UE may receive several control signalssuch as PDCCH signals from the plurality of small cells andsimultaneously or separately receive PDCCH signals, which are data, fromthe plurality of small cells. The UE may include one or more receiversfor receiving data from the plurality of small cells. As such receivers,a minimum mean square error-interference rejection combining (MMSE-IRC)receiver for efficiently eliminating interference among the plurality ofcells may be used. The UE may notify each cell of information aboutreceiver performance in an initial cell connection step of each cell.

The signal received via the MMSE-IRC receiver may be expressed as shownin Equation 7 below. At this time, a system using N_(TX) transmitantennas and N_(RX) receive antennas is assumed.

$\begin{matrix}{{r\left( {k,l} \right)} = {{{H_{1}\left( {k,l} \right)}{d_{1}\left( {k,l} \right)}} + {\sum\limits_{j = 2}^{N_{BS}}\; {{H_{j}\left( {k,l} \right)}{d_{j}\left( {k,l} \right)}}} + {n\left( {k,l} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 4, k means a k-th subcarrier of a specific subframe and lmeans an l-th OFDM symbol. In Equation 4 below, H_(l)(k,l)d_(l)(k,l)denotes a preferred signal received by the UE and H_(j)(k,l)d_(j)(k,l)denotes an interference signal transmitted from a j-th (j>l) eNB. Atthis time, H_(l)(k,l) and H_(j)(k,l) respectively mean estimated radiochannels, d_(j)(k,l) denotes a N_(Tx)×1 transmission data vector andn(k,l) denotes noise. {circumflex over (d)}_(l)(k,l) is a restored datasignal when rank is N_(stream) and may be expressed as shown in Equation5 below.

{circumflex over (d)} _(l)(k,l)=W _(RX,l)(k,l)r(k,l)  [Equation 5]

In Equation 5, W_(RX,1)(k,l) denotes a N_(Stream)×N_(Rx) receiver weightmatrix. In the MMSE-IRC receiver, W_(RX,l)(k,l) may be computed as shownin Equation 6 below.

W _(RX,l)(k,l)=Ĥ _(l) ^(H)(k,l)R ⁻¹  [Equation 6]

At this time, R may be computed using a transmitted DM-RS as shown inEquation 7 below.

$\begin{matrix}{R = {{{P_{1}{{\hat{H}}_{1}\left( {k,l} \right)}{{\hat{H}}_{1}^{H}\left( {k,l} \right)}} + {\frac{1}{N_{sp}}{\sum\limits_{k,{l \in {{DM} - {RS}}}}\; {{\overset{\sim}{r}\left( {k,l} \right)}{\overset{\sim}{r}\left( {k,l} \right)}^{H}{\overset{\sim}{r}\left( {k,l} \right)}}}}} = {{r\left( {k,l} \right)} - {{{\hat{H}}_{1}\left( {k,l} \right)}{d_{1}\left( {k,l} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

In Equation 10, Ĥ_(l)(k,l) denotes an estimated radio channel, N_(sp)denotes the number of samples of the DM-RS, and P1 denotes transmitpower. In addition, r(k,l) denotes a transmitted DM-RS and {tilde over(r)}(k,l) denotes an estimated DM-RS.

3.3 PUSCH Resource Scheduling Method in Small Cell Environment

Assume that the embodiments of the present invention are performed in awireless environment in which it is difficult to share schedulinginformation between small cells in real time. Accordingly, when thesmall cells perform scheduling of the UE, the radio resources used forthe PUSCH by the small cells may overlap. In this case, the UEtransmitting a PUSCH signal to a specific small cell may causeinterference with another small cell, thereby deteriorating PUSCHreception performance.

Accordingly, in order to avoid such a phenomenon, the PUSCH regionsassigned to the UE by two or more small cells configuring themulti-connectivity mode may be assigned so as not to overlap. Forexample, the small cells may divide PUSCH resources in the time domainor the frequency domain or may divide the PUSCH resources in the spatialdomain if multiple antennas are supported. When the PUSCH resources aredivided in the spatial domain, PUSCH transmission may be restricted torank 1 in order to eliminate the interference signal. Information on thePUSCH resources divided in the time domain, the frequency domain, and/orthe spatial domain may be shared in advance or at a long period via awired or wireless link between scheduling cells.

In this case, two or more small cells may schedule PUSCH resources orPUCCH resources and transmit a PDCCH signal or E-PDCCH signal includinguplink resource assignment information to the UE. The UE in themulti-connectivity mode may transmit a scheduling request (SR) via theuplink resource assignment region assigned by each of the two or moresmall cells.

4. Power Control Method in Multi-Connectivity Mode

4.1 PUSCH Transmit Power

In the multi-connectivity mode, PUSCH scheduling may be individuallyperformed in several cells. Accordingly, ACK/NACK information of a PUSCHor CSI information for PDSCH scheduling is preferably transmitted toeach cell. This is because the physical positions of scheduling cellsare different and thus small cells in the multi-connectivity mode cannotshare scheduling information in real time. Accordingly, a PUSCH signalfor transmitting ACK/NACK or periodic CSI may be configured at a higherlayer of an eNB and/or a UE to be transmitted to each small cell. Whenthe PUCCH signal is configured to be transmitted to each small cell, thetransmit power of the PUSCH signal may be determined as shown inEquation 8 below.

$\begin{matrix}{{P_{{PUSCH},c}(i)} = {\min \begin{Bmatrix}{{10\mspace{11mu} {\log_{10}\left( {{{\hat{P}}_{{CMAX},c}(i)} - {\sum\limits_{c}\; {{\hat{P}}_{{PUCCH},c}(i)}}} \right)}},} \\{{10\mspace{11mu} {\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O\; \_ \; {PUSCH}},c}(j)} +} \\{{{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} + {f_{c}(i)}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

where, {circumflex over (P)}_(CMAX,c)(i) denotes the linear value ofP_(CMAX,c)(i) which is maximum transmit power in an i-th subframe of aserving cell c set at a higher layer, {circumflex over (p)}_(PUCCH,c)(i)denotes the linear value of F_(PUCCH,c)(i) of a PUCCH transmitted in thei-th subframe of the serving cell M_(PUSCH,c)(i) denotes the number ofresource blocks (RBs) assigned for PUSCH signal transmission in the i-thsubframe of the serving cell c, P₀ _(FUSCH) _(,c)(j) denotes a sum of P₀_(—NOMINAL—PUSCH) _(,c)(j) which is a cell-specific parameter set at thehigher layer and P₀ _(—) _(UE) _(—) _(PUSCH,c)(j) which is a UE-specificparameter set at the higher layer, α_(c)(j) denotes a value set at theserving cell c, PL_(c) denotes the path loss value of the serving cellc, Δ_(TF,c)(i) denotes a value changed according to MCS value, andf_(c)(i) denotes a value corresponding to a power control commandtransmitted via a downlink control channel. That is, the PUSCH transmitpower of the serving cell c may be determined using the remaining powerother than the PUCCH transmit power transmitted at all the other servingcells.

In Equation 8, the path loss of the serving cell c may be measured asshown in Equation 9 below.

PL _(c)=referenceSignalPower−higher layer filtered RSRP  [Equation 9]

At this time, when the serving cell, to which the UE will transmit thePUCCH, does not belong to a timing advanced group (TAG), to which aprimary cell belongs, the eNB may configure a reference cell to be usedto measure path loss at the higher layer. At this time, a high layerfiltered RSRP may be calculated as shown in FIG. 10 below.

F _(n)=(1−a)·F _(n-1) +a·M _(n)  [Equation 10]

In Equation 10, M_(n) denotes a most recently received measurementvalue, F_(n) denotes a filtered measurement value modified based on thereceived measurement result, F_(n-1) denotes a previous filteredmeasurement value, a=½^((k/4)), and k denotes a constant value set at ahigher layer. Accordingly, M_(n) denotes an RSRP value measured andtransmitted by a physical layer.

4.2 PUCCH Transmit Power Control Method—1

When the UE in the multi-connectivity mode is configured to transmit thePUCCH to several small cells, the transmit power of the PUCCHtransmitted to the small cell c (that is, the serving cell c) may bedetermined as shown in Equation 11 below.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min \begin{Bmatrix}{{P_{{CMAX},c}(i)},} \\{P_{{0\_ \; {PUCCH}},c} + {PL}_{c} + {h_{c}\left( {n_{CQI},n_{HARQ},n_{SR}} \right)} +} \\{{\Delta_{F\; \_ \; {PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g_{c}(i)}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

When the PUCCH is not transmitted in the subframe i of the small cell c,for a PUCCH transmit power control (TPC) command transmitted via DCIformat 3 or 3A, the UE may assume that the transmit power of the PUCCHin the subframe i is calculated as shown in Equation 12 below.

P _(PUCCH,c)(i)=min {P _(CMAX,c)(i),P ₀ _(—) _(PUCCH,c) +PL_(c)+g_(c)(i)}  [Equation 12]

At this time, P_(CMAX,c)(i) denotes a value defined as the maximumtransmit power of the UE in the subframe i of the small cell c.

Here, P₀ _(—) _(PUCCH,c) denotes a parameter indicating a sum of P₀ _(—)_(NOMINAL) _(—) _(PUCCH,c) which is a cell-specific parameter set withrespect to the small cell c at the higher layer and P₀ _(—) _(UE) _(—)_(PUCCH,c) which is a UE-specific parameter.h_(c)(n_(CQI),n_(HARQ),n_(SR)) denotes a value determined according tothe PUCCH format of the small cell c. At this time, n_(CQI), n_(HARQ),n_(SR) respectively denote a CQI bit number, a HARQ ACK/NACK informationbit number, and an SR information bit number, which are determineddepending on whether CQI, ACK/NACK and/or SR are transmitted. Inaddition, Δ_(F) _(—) _(PUCCH)(F) denotes a value set at the higher layeraccording to the PUCCH format and Δ_(TxD)(F′) denotes a value set at thehigher layer when the PUCCH is transmitted using two antenna ports andis set to “0” when the PUSCH is transmitted using a single antenna port.In addition, g_(c)(i) denotes a value which may be acquired from a PUCCHtransmit power control command transmitted via a downlink controlchannel. At this time, P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) and P₀ _(—)_(UE) _(—) _(PUCCH,c) used in Equation 11 may be set using the followingmethods.

(1) Method 1: P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) and P₀ _(—) _(UE) _(—)_(PUCCH,c) are independently set at the serving cells configuring themulti-connectivity mode.

(2) Method 2: P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) is commonly used atseveral cells and P₀ _(—) _(UE) _(—) _(PUCCH,c) may be differently setaccording to cells.

(3) Method 3: P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) may be differently setaccording to cells and P₀ _(—) _(UE) _(—) _(PUCCH,c) may be commonly setwith respect to cells.

(4) Method 4: P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) and P₀ _(—) _(UE) _(—)_(PUCCH,c) may be commonly set with respect to the cells configuring themulti-connectivity mode.

When P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) and P₀ _(—) _(UE) _(—)_(PUCCH,c) are set according to the above-described described methods,the small cells configuring the multi-connectivity mode may share atleast one of P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) and P₀ _(—) _(UE) _(—)_(PUCCH,c) via a wired and/or wireless link. For example, the smallcells may share P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) in Method 2, mayshare P₀ _(—) _(UE) _(—) _(PUCCH,c) in Method 3, and may share bothvalues in Method 4.

However, the small cells in the multi-connectivity mode are connectedvia a non-ideal backhaul and thus cannot share scheduling information inreal time. Accordingly, the above-described parameter values may beshared between a plurality of small cells when entering themulti-connectivity mode or periodically.

When the UE transmits the PUCCH signal to the small cells in themulti-connectivity mode, in Equation 11, P_(CMAX,c)(i) indicating themaximum transmit power of the UE may be set according to cells. At thistime, operation of the UE upon reaching the maximum power or minimumpower according to cells may be defined. For example, when the PUCCHtransmit power for a specific cell of the small cells reaches a maximumor minimum power value, the UE may ignore a power increasing/decreasingcommand transmitted via the PDCCH signal.

4.3 PUCCH Transmit Power Control Method—2

In the following embodiments of the present invention, assume that thesmall cells (that is, scheduling cells) configuring themulti-connectivity mode are close to each other and arenetwork-synchronized with each other. That is, the UE may be configuredto transmit a PUCCH signal to a plurality of small cells in themulti-connectivity mode using one uplink resource region. In this case,the PUCCH transmit power may be set to a maximum value of the powervalues for receiving the PUCCH by each small as shown in Equation 13below.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min \begin{Bmatrix}{{\min\limits_{c}\; {P_{{CMAX},c}(i)}},} \\{{\max\limits_{c}P_{{0\_ \; {PUCCH}},c}} + {\max\limits_{c}{PL}_{c}} + {h\left( {n_{CQI},n_{HARQ},n_{SR}} \right)} +} \\{{\Delta_{F\; \_ \; {PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {\max\limits_{c}{g_{c}(i)}}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In Equation 13,

$\min\limits_{c}{P_{{CMAX},c}(i)}$

means a transmit power value defined in the small cell c having smallesttransmit power in the subframe i among the small cells in themulti-connectivity mode,

$\max\limits_{c}P_{{0\_ \; {PUCCH}},c}$

denotes a value of a small cell c having a largest sum of P₀ _(—)_(NOMINAL) _(—) _(PUCCH,c) and P₀ _(—) _(UE) _(—) _(PUCCH,c) among thesmall cells in the multi-connectivity mode, a path loss value

$\max\limits_{c}{PL}_{c}$

denotes a downlink path loss value corresponding to highest path lossamong path losses measured from a plurality of downlink channels. Inaddition, h(n_(CQI),n_(HARQ),n_(SR)) denotes a value changed accordingto the PUCCH format configured in the small cell c. For the small cellc, a value

$\max\limits_{c}{g_{c}(i)}$

is set to the largest value of values g_(c)(i) calculated as shown inEquation 14 below.

$\begin{matrix}{{g_{c}(i)} = {{g_{c}\left( {i - 1} \right)} + {\sum\limits_{m = 0}^{M - 1}\; {\delta_{PUCCH}\left( {i - k_{m}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

In Equation 14, g_(c)(i) is a value acquired by a PUCCH power controlcommand transmitted via a downlink control channel, that is, means acurrent PUCCH power control adjustment state in the i-th subframe of thesmall cell c and g(0) means an initial value after resetting. At thistime, δ_(PUCCH) is a UE-specific correction value and is a dB valueaccording to a TPC command included in the PDCCH.

In another aspect of the present invention, the PUCCH transmit power maybe calculated using the method shown in Equation 15 below instead ofEquation 13.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min \begin{Bmatrix}{{\min\limits_{c}{P_{{CMAX},c}(i)}},} \\{{\max\limits_{c}P_{{0\_ \; {PUCCH}},c}} + {\max\limits_{c}{PL}_{c}} + {h\left( {n_{CQI},n_{HARQ},n_{SR}} \right)} +} \\{{\Delta_{F\; \_ \; {PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g_{c}(i)}}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

For the parameter values used in Equation 15, refer to the descriptionof the parameters shown in Equations 11 to 13. In Equation 15, a valueg_(c)(i) may be calculated as shown in Equation 16 or 17 below.

$\begin{matrix}{{g(i)} = {{g\left( {i - 1} \right)} + {\sum\limits_{m = 0}^{M - 1}\; {\max\limits_{c}{\delta_{{PUCCH},c}\left( {i - k_{m}} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack \\{{g(i)} = {{g\left( {i - 1} \right)} + {\max\limits_{c}{\sum\limits_{m = 0}^{M - 1}\; {\delta_{{PUCCH},c}\left( {i - k_{m}} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

Equation 16 shows a method for calculating a value g_(c)(i) of the smallcell c having a largest value δ_(PUCCH) among the small cells in themulti-connectivity method and Equation 17 shows a method for calculatinga value g_(c)(i) of the small cell c having a largest sum of δ_(PUCCH).

4. 4 PUCCH Transmit Power Control Method—3

In the following embodiments of the present invention, assume that thesmall cells (that is, scheduling cells) configuring themulti-connectivity mode are close to each other and arenetwork-synchronized with each other. That is, the UE may be configuredto transmit a PUCCH signal to a plurality of small cells in themulti-connectivity mode using one uplink resource region. In this case,a plurality of scheduling cells may receive the PUCCH transmitted by theUE via the resource region.

At this time, the plurality of small cells may transmit power controlcommands for a single PUCCH to the UE. When the UE receives a commandfor increasing transmit power from one small cell, the UE preferablyincreases PUCCH power for stable reception of the PUCCH information. Inaddition, when commands for decreasing transmit power are received fromall small cells, the UE preferably decreases PUCCH power.

When the power control command for increasing power to exceedP_(CMAX,c)(i) of an arbitrary small cell c is received, the UE maymaintain transmit power regardless of the power control commands ofdifferent small cells. That is, if the value P_(CMAX,c)(i) isdifferently set according to small cells, when the transmit powerreaches a value corresponding to

$\min\limits_{c}{P_{{CMAX},c}(i)}$

(the minimum value of P_(CMAX,c)(i) set per cell), the command forincreasing the transmit power from the arbitrary small cell is ignoredand the transmit power is maintained.

In addition, when a power control command for performing transmission toan arbitrary serving cell with power less than minimum transmit power isreceived, the UE may maintain transmit power without decreasing thetransmit power when all the power control commands of the other smallcells indicate decrease in transmit power. At this time, when any onesmall cell transmits a power control command for increasing power, theUE increases transmit power. When the PUCCH is not transmitted, thePUCCH power control command transmitted via DCI format 3/3A is used tocalculate the transmit power of the subframe i using Equation 18 below.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min \left\{ {{\begin{matrix}\min \\c\end{matrix}{P_{{CMAX},c}(i)}},{P_{0\_ \; {PUCCH}} + {PL}_{c} + {g_{c}(i)}}} \right\}}} & {{Equation}\mspace{14mu} 18}\end{matrix}$

Equation 18 shows a method for calculating PUCCH transmit power withrespect to a small cell c having a smallest maximum transmit power of aplurality of small cells currently configuring the multi-connectivitymode.

4.5 PUCCH Transmit Power Calculation Method

Hereinafter, a method for calculating PUCCH transmit power based on thePUCCH transmit power control methods described in Chapters 4.2 to 4.4will be described.

FIG. 17 is a diagram showing one method for calculating PUCCH transmitpower.

A UE and two or more small cells may configure a multi-connectivitymode. For the multi-connectivity mode, refer to Chapter 3 (S1710).

The UE may receive higher layer signals from the two or more smallcells. At this time, the higher layer signals may include first powerparameters set at the higher layer of each small cell. At this time, thefirst power parameters may include one or more of P₀ _(—) _(NOMINAL)_(—) _(PUCCH,c), P₀ _(—) _(UE) _(—) _(PUCCH,c), Δ_(F) _(—) _(PUCCH)(F)and Δ_(TxD)(F′) (S1720).

In addition, the UE may receive a PDCCH signal including second powerparameters from the two or more small cells, respectively in eachsubframe. At this time, the second power parameters may includeg_(c)(i), δ_(PUCCH) and a parameter indicating a PUCCH format (S1730).

In addition, the UE may calculate the path loss values of the two ormore small cells (S1740).

The UE may calculate the PUCCH transmit power using the methods shown inEquations 13 to 18 based on the first power parameters, the second powerparameters and the path loss values respectively received in stepsS1720, S1730 and S1740.

4.5 Power Headroom Reporting Method

The UE notifies the eNB (that is, the small cell or the marco cell) ofthe transmit power state thereof in the form of a power headroom report(PHR). The PHR may include two reporting types, that is, type 1 and type2. At this time, the type 1 PHR indicates a method for calculating powerheadroom on the assumption that a UE transmits only a PUSCH and the type2 PHR indicates a method for calculating power headroom on theassumption that a UE transmits both a PUSCH and a PUCCH.

As described above, since the UE may be configured to transmit ACK/NACKor CSI to several small cells using the PUCCH in the multi-connectivitymode, the type 2 PRH may be configured to be transmitted to severalsmall cells.

If such PUCCH power control is assumed, when the PUSCH and the PUCCH aresimultaneously transmitted to the small cell c in the subframe i, thetype 2 PHR of the serving cell c may be calculated as shown in Equation19 below.

$\begin{matrix}{{{PH}_{{{type}\; 2},c}(i)} = {{P_{{CMAX},c}(i)} - {10\; {\log_{10}\begin{pmatrix}{10^{{(\begin{matrix}{{10\; {\log_{10}{({M_{{PUSCH},c}{(i)}})}}} + {P_{{O\; \_ \; {PUSCH}},c}{(j)}} +} \\{{{\alpha_{c}{(j)}} \cdot {PL}_{c}} + {\Delta_{{TF},c}{(i)}} + {f_{c}{(i)}}}\end{matrix})}/10} +} \\10^{{(\begin{matrix}{P_{{0\_ \; {PUCCH}},c} + {PL}_{c} + {h_{c}{({n_{CQI},n_{HARQ},n_{SR}})}} +} \\{{\Delta_{F\; \_ \; {PUCCH}}{(F)}} + {\Delta_{TxD}{(F^{\prime})}} + {g_{c}{(i)}}}\end{matrix})}/10}\end{pmatrix}}}}} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

If only the PUSCH is transmitted to the small cell c in the subframe i,the type 2 PHR may be calculated as shown in Equation 20 below.

$\begin{matrix}{{{PH}_{{{type}\; 2},c}(i)} = {{P_{{CMAX},c}(i)} - {10\; {\log_{10}\begin{pmatrix}{10^{{(\begin{matrix}{{10\; {\log_{10}{({M_{{PUSCH},c}{(i)}})}}} + {P_{{O\; \_ \; {PUSCH}},c}{(j)}} +} \\{{{\alpha_{c}{(j)}} \cdot {PL}_{c}} + {\Delta_{{TF},c}{(i)}} + {f_{c}{(i)}}}\end{matrix})}/10} +} \\10^{{({P_{{0\_ \; {PUCCH}},\; c} + {PL}_{c} + {g_{c}{(i)}}})}/10}\end{pmatrix}}}}} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack\end{matrix}$

In addition, when only the PUCCH is transmitted to the small cell c inthe subframe i, the type 2 PHR may be calculated as shown in Equation 21below.

$\begin{matrix}{{{PH}_{{{type}\; 2},c}(i)} = {{P_{{CMAX},c}(i)} - {10\; {\log_{10}\begin{pmatrix}{10^{{({{P_{{O\; \_ \; {PUSCH}},c}{(1)}} + {{\alpha_{c}{(1)}} \cdot {PL}_{c}} + {f_{c}{(i)}}})}/10} +} \\10^{{(\begin{matrix}{P_{{0\_ \; {PUCCH}},c} + {PL}_{c} + {h_{c}{({n_{CQI},n_{HARQ},n_{SR}})}} +} \\{{\Delta_{F\; \_ \; {PUCCH}}{(F)}} + {\Delta_{TxD}{(F^{\prime})}} + {g_{c}{(i)}}}\end{matrix})}/10}\end{pmatrix}}}}} & \left\lbrack {{Equation}\mspace{14mu} 21} \right\rbrack\end{matrix}$

In addition, when the PUSCH and the PUCCH are not transmitted to thesmall cell c in the subframe i, the type 2 PHR may be calculated asshown in Equation 22 below.

$\begin{matrix}{{{PH}_{{{type}\; 2},c}(i)} = {{{\overset{\sim}{P}}_{{CMAX},c}(i)} - {10\mspace{11mu} {\log_{10}\begin{pmatrix}{10^{{({{P_{{O\; \_ \; {PUSCH}},c}{(1)}} + {{\alpha_{c}{(1)}} \cdot {PL}_{c}} + {f_{c}{(i)}}})}/10} +} \\10^{{({P_{{0\_ \; {PUCCH}},c} + {PL}_{c} + {g_{c}{(i)}}})}/10}\end{pmatrix}}}}} & \left\lbrack {{Equation}\mspace{14mu} 22} \right\rbrack\end{matrix}$

At this time, {tilde over (P)}_(CMAX,c)(i) is a value calculated on theassumption of MPR=0 dB, A-MPR=0 dB, P-MPR=0 dB and ΔT_(C)=0 dB.

5. Apparatuses

Apparatuses illustrated in FIG. 18 are means that can implement themethods described before with reference to FIGS. 1 to 17.

A UE may act as a transmitter on a UL and as a receiver on a DL. An eNBmay act as a receiver on a UL and as a transmitter on a DL.

That is, each of the UE and the eNB may include a Transmission (Tx)module 1840 or 1850 and a Reception (Rx) module 1860 or 1870, forcontrolling transmission and reception of information, data, and/ormessages, and an antenna 1800 or 1810 for transmitting and receivinginformation, data, and/or messages.

Each of the UE and the eNB may further include a processor 1820 or 1830for implementing the afore-described embodiments of the presentdisclosure and a memory 1880 or 1890 for temporarily or permanentlystoring operations of the processor 1820 or 1830.

The embodiments of the present invention may be performed using thecomponents and functions of the above-described UE and eNB. For example,the processor of the UE may calculate PUSCH transmit power or PUCCHtransmit power using the methods described in Chapters 1 to 4. At thistime, the processor is connected to the transmitter and the receiver totransmit and receive parameters necessary to calculate transmit power.For a detailed description thereof, refer to Chapters 1 to 4.

The Tx and Rx modules of the UE and the eNB may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDMA packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the eNB of FIG. 18may further include a low-power Radio Frequency (RF)/IntermediateFrequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory1880 or 1890 and executed by the processor 1820 or 1830. The memory islocated at the interior or exterior of the processor and may transmitand receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to various wireless access systemsincluding a 3GPP system, a 3GPP2 system, and/or an IEEE 802.xx system.Besides these wireless access systems, the embodiments of the presentdisclosure are applicable to all technical fields in which the wirelessaccess systems find their applications.

1. A method for controlling uplink transmit power of a user equipment(UE) in a radio access system supporting a multi-connectivity mode, themethod performed by the UE and comprising: calculating physical uplinkcontrol channel (PUCCH) transmit power for two or more small cells inthe multi-connectivity mode; and transmitting respective PUCCH signalsto the two or more small cells based on the PUCCH transmit power,wherein, in the multi-connectivity mode, the UE maintains multipleconnections with the two or more small cells, and wherein the two ormore small cells are connected to each other via a non-ideal backhaullink.
 2. The method according to claim 1, further comprising: receivingtwo or more higher layer signals including first power parameters fromthe two or more small cells; receiving two or more physical downlinkcontrol channel (PDCCH) signals including second power parameters fromthe two or more small cells; and measuring path loss values of the twoor more small cells, wherein the PUCCH transmit power is calculatedbased on the first power parameters, the second power parameters and thepath loss values.
 3. The method according to claim 2, wherein the PUCCHtransmit power is calculated by:${P_{PUCCH}(i)} = {\min \begin{Bmatrix}{{P_{{CMAX},c}(i)},} \\{P_{{0\_ \; {PUCCH}},c} + {PL}_{c} + {h_{c}\left( {{n_{{CQI},}n_{HARQ}},n_{SR}} \right)} +} \\{{\Delta_{F\; \_ \; {PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g_{c}(i)}}\end{Bmatrix}}$ where, P_(CMAX,c)(i) denotes maximum transmit power in asubframe i of a small cell c, P₀ _(—) _(PUCCH,c) denotes a sum of P₀_(—) _(NOMINAL) _(—) _(PUCCH,c) which is a cell-specific parameter setwith respect to the serving cell c at a higher layer and P₀ _(—) _(UE)_(—PUCCH,c) which is a UE-specific parameter,h_(c)(n_(CQI),n_(HARQ),n_(SR)) denotes a parameter depending on a PUCCHformat of the small cell c, n_(CQI), n_(HARQ), and n_(SR) respectivelydenoting channel status information (CQI) bit number, ACK/NACKinformation bit number, and scheduling request (SR) information bitnumber, Δ_(F) _(—) _(PUCCH)(F) denotes a value set at the higher layeraccording to a PUCCH format, Δ_(TxD)(F′) denotes a value set at thehigher layer to be used when the UE transmits the PUCCH signals via twoantenna ports, g_(c)(i) denotes a value acquired from a PUCCH powercontrol command transmitted via a physical downlink control channel(PDCCH) signal, and c denotes an index of each of the two or more smallcells in the multi-connectivity mode.
 4. The method according to claim3, wherein P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) is a value commonly setwith respect to the two or more small cells and P₀ _(—) _(UE) _(—)_(PUCCH,c) is a value individually set with respect to the two or moresmall cells.
 5. The method according to claim 3, wherein P₀ _(—)_(NOMINAL) _(—) _(PUCCH,c) is a value individually set with respect tothe two or more small cells and P₀ _(—) _(UE) _(—) _(PUCCH,c) is a valuecommonly set with respect to the two or more small cells.
 6. The methodaccording to claim 3, wherein the first power parameters include atleast one of P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c),P₀ _(—) _(UE) _(—)_(PUCCH,c), Δ_(F) _(—) _(PUCCH)(F) and Δ_(TxD)(F′).
 7. The methodaccording to claim 3, wherein the second power parameters includeg_(c)(i), δ_(PUCCH) and a parameter indicating a PUCCH format.
 8. A userequipment (UE) for controlling uplink transmit power in a radio accesssystem supporting a multi-connectivity mode, the UE comprising: atransmitter; a receiver; and a processor connected to the transmitterand the receiver to control the uplink transmit power, the processor isconfigured to: calculate physical uplink control channel (PUCCH)transmit power for two or more small cells in the multi-connectivitymode, and control the transmitter to transmit respective PUCCH signalsto the two or more small cells based on the PUCCH transmit power,wherein, in the multi-connectivity mode, the UE maintains multipleconnections with the two or more small cells, and wherein the two ormore small cells are connected to each other via a non-ideal backhaullink.
 9. The UE according to claim 8, wherein the processor isconfigured to: control the receiver to receive two or more higher layersignals including first power parameters from the two or more smallcells; control the receiver to receive two or more physical downlinkcontrol channel (PDCCH) signals including second power parameters fromthe two or more small cells; and measure path loss values of the two ormore small cells, wherein the PUCCH transmit power is calculated basedon the first power parameters, the second power parameters and the pathloss values.
 10. The UE according to claim 9, wherein the PUCCH transmitpower is calculated by: ${P_{PUCCH}(i)} = {\min \begin{Bmatrix}{{P_{{CMAX},c}(i)},} \\{P_{{0\_ \; {PUCCH}},c} + {PL}_{c} + {h_{c}\left( {{n_{{CQI},}n_{HARQ}},n_{SR}} \right)} +} \\{{\Delta_{F\; \_ \; {PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g_{c}(i)}}\end{Bmatrix}}$ where, P_(CMAX,c)(i) denotes maximum transmit power in asubframe i of a small cell c, P₀ _(—) _(PUCCH,c) denotes a sum of P₀_(—) _(NOMINAL) _(—) _(PUCCH,c) which is a cell-specific parameter setwith respect to the serving cell c at a higher layer and P₀ _(—) _(UE)_(—) _(PUCCH,c) which is a UE-specific parameter,h_(c)(n_(CQI),n_(HARQ),n_(SR)) denotes a parameter depending on a PUCCHformat of the small cell c, n_(CQI), n_(HARQ) and n_(SR) respectivelydenoting channel status information (CQI) bit number, ACK/NACKinformation bit number, and scheduling request (SR) information bitnumber, Δ_(F) _(—) _(PUCCH)(F) denotes a value set at the higher layeraccording to a PUCCH format, Δ_(TxD)(F) denotes a value set at thehigher layer to be used when the UE transmits the PUCCH signals via twoantenna ports, g_(c)(i) denotes a value acquired from a PUCCH powercontrol command transmitted via a physical downlink control channel(PDCCH) signal, and c denotes an index of each of the two or more smallcells in the multi-connectivity mode.
 11. The UE according to claim 9,wherein P₀ _(—) _(NOMINAL) _(—) _(PUCCH,c) is a value commonly set withrespect to the two or more small cells and P₀ _(—) _(UE) _(—) _(PUCCH,c)is a value individually set with respect to the two or more small cells.12. The UE according to claim 9, wherein P₀ _(—) _(NOMINAL) _(—)_(PUCCH,c) is a value individually set with respect to the two or moresmall cells and P₀ _(—) _(UE) _(—PUCCH,c) is a value commonly set withrespect to the two or more small cells.
 13. The UE according to claim 9,wherein the first power parameters include at least one of P₀ _(—)_(NOMINAL) _(—) _(PUCCH,c), P₀ _(—) _(UE) _(—) _(PUCCH,c), Δ_(F) _(—)_(PUCCH,c)(F) Δ_(TxD)(F′).
 14. The UE according to claim 9, wherein thesecond power parameters include g_(c)(i), δ_(PUCCH) and a parameterindicating a PUCCH format.